Passivation via atomic layer deposition Al2O3 for the performance enhancement of quantum dot photovoltaics

PbS colloidal quantum dot solar cells (CQDSCs) are promising photovoltaic devices with a broad spectral response, solution processability and long-term air stability. Recently, major progresses have been achieved in the performance enhancement of CQDSCs through the chemical surface passivation of CQDs and the device engineering. However, the p-type PbS-EDT hole extraction layer presents high surface-trap density, which induces charge recombination risk and blocks the hole extraction at the PbS-EDT/Au interface. Herein, we demonstrated a method to passivate the surface traps of PbS-EDT film by post-depositing an aluminum oxide (Al2O3) layer using atomic layer deposition (ALD) technology. The ALD progress was carefully controlled to ensure that ALD Al2O3 could overcoat and infill the PbS-EDT film at the same time. This ALD Al2O3 treatment efficiently passivated the surface traps of PbS-EDT and successfully kept the proper band alignment at PbS-TBAI/PbS-EDT interface for the fast hole extraction of CQDSCs. Consequently, this method allowed the efficient carrier extraction at the PbS-EDT/Au interface through suppressing trap-induced reverse Schottky barrier. A power conversion efficiency of 7.07% was finally obtained in the PbS CQDSCs with ALD Al2O3.